1. Field of the Invention
The present invention relates to a radio control device (gear) for remotely manipulating radio controlled models.
2. Description of the Prior Art
Nowadays, radio-control devices (hereinafter referred to as R/C devices) are used for various radio controlled models (hereinafter referred to as R/C models) such as model aircraft, model helicopters, model vehicles, model boats and others. For them, two types of main carrier wave modulation scheme, that is, AM (Amplitude Modulation) and FM (Frequency Modulation) are used or two types of main carrier wave modulation signal conversion scheme, that is, PPM (Pulse Position Modulation) and PCM (Pulse Code Modulation) are used.
Regarding the R/C devices, the frequency bands for carriers and frequencies in each frequency band, allowable in each country, are regulated by laws, statutes, and rules (“the Radio Law”) specific to each country in which the devices are operated. For example, the frequency bands usable in Japan are 27 MHz band, 40 MHz band, and 72 MHz band, each in which plural frequencies are determined.
When plural radio controlled models are used in the same area at the same time, the frequency not used by other radio controlled models must be selected in order to avoid interference. Typically, a crystal oscillator (referred to as quartz) is changed to select a different band and change the carrier frequency.
Recently, the frequency synthesizer scheme employing the PLL (Phase Locked Loop) circuit generally used in the communication fields has been adopted and is in broad use. Such a frequency synthesizer scheme can set the carrier to different frequencies by changing the frequency division ratio. However, the use of the R/C device in the frequency synthesizer scheme depends on regulation by the Radio Law in each country. Moreover, even in countries allowing the use of the frequency synthesizer scheme, frequencies other than designated frequencies cannot be used.
Japanese Utility Model publication No. Zikkai-hei 6-31232, filed by the present applicant, discloses a conventional transmitter to solve the above-mentioned problem. The transmitter has a configuration in which a crystal high-frequency module or a PLL high-frequency module is attachable to or detachable from the transmitter. For that reason, in countries applying and not applying the frequency synthesizer scheme in compliance with different legal systems, a common transmitter can be used without preparing different transmitters.
The PLL high-frequency module has memory that stores frequency data to variably control the carrier wave frequency. Hence, when high-frequency modules, each having a memory that stores frequency data by country, are prepared, the frequency synthesizer scheme using a carrier wave of a predetermined frequency can be applied for the transmitter through an exchange of the module.
In the receiver, the crystal oscillator is replaced to avoid the interference of receiving frequencies possible in the same area, in a manner similar to that of the transmitter. However, since spare crystal oscillators have to be available, receivers in a frequency synthesizer scheme, each incorporating a PLL circuit, are being used widely. In that receiver, the frequency can be easily changed and adjusted by varying the frequency division ratio of the frequency divider through a changeover operation of a DIP switch disposed in the receiver body. However, while the radio controlled model is operating, the switch may change due to a function of some kind such as the vibration of an engine, thus varying the frequency division ratio. As a result, the receiving frequency can inadvertently switch over so that the radio-controlled model becomes uncontrollable during operation.
In order to solve such a problem, Japanese Utility Model No. Tokkai-hei 9-9697, filed by the present applicant, discloses a receiver for radio controlled models in a frequency synthesizer scheme using a conventional PLL circuit. In the receiver, two DIP switches, for example, which are disposed therein, selects a predetermined frequency from among predetermined plural sets of frequency data. When the power source is turned on, the receiver checks a usable frequency group and then captures the selected band information. The receiver determines whether or not the frequency data corresponding to the band information is a normal frequency. In the discrimination result, the frequency division ratio of the frequency divider in the PLL circuit is determined based on the frequency data stored in the memory. The frequency locked on based on the frequency division ratio is set to a fixed value as a receiving frequency until the power source is turned off at the next stage. For that reason, the possibility does not occur that the receiving frequency once set changes unintentionally due to disturbance such as the vibration or erroneous operation. As a result, the reliability can be improved.
In the radio controlled model in the frequency synthesizer scheme incorporating a PLL circuit, the receiver mounted in the radio controlled model is taken out to vary, for example, the receiving frequency. The switch such as a DIP switch disposed in the receiver body is manually operated to change the frequency division ratio. Thus the receiving frequency is changed.
The switch is disposed in the housing of the radio controlled model while the receiver is wrapped or covered with a vibration-proof and water-proof rubber. Thus, a change of receiving frequency data or a failure of the radio controlled model, caused by a changeover of the switch of the receiver due to conditions, such as vibrations of the engine in to the model body or water leakage, is prevented.
Such a configuration has a disadvantage in the frequency changing work. That is, when the receiving frequency is forced to change because a set frequency has been already used, the receiver is first taken out of the radio controlled model. Then, the vibration-proof or water-proof material such as rubber is uncovered to perform the frequency switching work. Finally, the receiver is again covered with the rubber and is stored inside the radio controlled model. This is troublesome and results in a time loss.